Subject:
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Re: A robot who knows his position (fwd)
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 28 Apr 1999 19:15:31 GMT
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Original-From:
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John A. Tamplin <JAT@stopspammersLIVEONTHENET.COM>
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Viewed:
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1153 times
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On Wed, 28 Apr 1999, Mario Ferrari wrote:
> > My flatmate has
> > informed me of a way the Chinese used to navigate before they had compasses.
> > Basically, you get a two wheeled vehicle, take the output of each wheel and
> > feed it into a differential such the differential is still when they are • moving
> > in the same direction. Take the output of the diff. and arrange it so that it
> > makes an arrow sticking out of the top of the contraption (think "weather
> > vane") turn. Down-gear this turning a bit. The result of this is the fact that
> > when you move the vehicle around, the "arrow" always stays pointing in a
> > direction parallel to it's original direction. I reckon you could use this
> > effect to tie into something external. Don't ask me what just yet ;-)
>
> Seems interesting. But you would still have problem with slippage...
> I think a magnetic or gyro compass would work better. Is there anybody around
> who did interface a compass to the RCX?
I have been thinking about a different approach. I have not actually built
anything to use it yet, but I believe it should work reasonably well.
The basic idea is similar to the old optical mouse pads -- draw
horizontal and vertical lines on the playing field. Use different colors
for the horizontal and vertical lines (easily distinguishable by the
light sensor's greyscale values). You can then compute relative position
changes and from that direction of travel. Obviously, the resolution you can
achieve is limited to the spacing of the lines and the accuracy of
measuring your bot's motion in between them, but it should be sufficient.
The difficulties come from distinguishing the lighter-colored line from the
fringe of the darker line, and the varying line widths depending on the
angle of travel relative to the line. For instance, travelling parallel
to one of the axes will result in no line crossings for that axis (or
continuously being on an axis).
You can use wider lines in the center of the playing field to give an
idea of absolute positon, or you can allow your bot to explore the
playing field determining the dimensions by bumper contact with the edge.
Clearly, this is only applicable in limited situations where you can mark
the area the bot will traverse.
John A. Tamplin Traveller Information Services
jat@LiveOnTheNet.COM 2104 West Ferry Way
256/705-7007 - FAX 256/705-7100 Huntsville, AL 35801
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 3 Replies:
 | | Inverting the robot position problem...
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| (...) This brings out a VERY interesting application. Most bots have trouble navigating a real maze because of obvious slippage problems and generally poor resolution of sensors. What about inverting the problem and printing (using your favorite (...) (26 years ago, 28-Apr-99, to lugnet.robotics)
| | | RE: A robot who knows his position (fwd)
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| (...) Just for reference: The optical mouse pads made by Mouse Systems, and shipped with Sun workstations for a long time, used two detectors in the mouse. One used a red LED, and the other one looked the same, but was dark. I suspect it was an IR (...) (26 years ago, 28-Apr-99, to lugnet.robotics)
| | | Re: A robot who knows his position (fwd)
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| (...) I like John's idea. You could combine it with odometry and get a very affordable and precise positioning system. I'm quite happy with the results of odometry in the short range, I mean until you accumulate too many small errors. My robot (...) (26 years ago, 29-Apr-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: A robot who knows his position (fwd)
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| (...) Looking forward to seeing them :) (...) Dead-reckoning should be used BETWEEN two consecutive (artificial) landmark sensing. When you get any external reference point you can zero your accumulated errors. (...) moving (...) Seems interesting. (...) (26 years ago, 28-Apr-99, to lugnet.robotics)
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